Tilt-shift lenses have some unusual abilities. "Tilt" means the focal plane can be tilted relative to the image plane of the camera. One popular usage of this ability is to make the foreground and background in focus without using a small aperture (large f-number). Another example is to have two people standing next to each other, but one is in focus and the other is not.
"Shift" means the center of the lens is not aligned with the center of the image sensor. A popular usage is to either eliminate or accentuate the convergence of parallel lines, as in tall buildings. Rent a tilt-shift camera lens with your next order to add some variety to your photo shoot.